This invention relates in general to soldering and in particular to a new and useful method and apparatus for reflow solder and reflow desoldering of circuit boards.
For reflow soldering circuit boards, a variety of infrared through-type furnaces are on the market. These have the following particular disadvantages: if due to a disturbance in the production process (during mounting or solder dosing) the installation must be turned off, it is possible that the material to be soldered is destroyed because of the larger amount of heat stored in the furnace. Furthermore, the material to be soldered is subject to continuous shaking and jarring during the transport in the melting and solidification area, which influence the strength and the metal structure of the solder sites negatively.
Known are, furthermore, halogen point radiators with gold-plated reflector, which are suitable for manually reduced operating voltage for reflow soldering of single soldering sites.
The invention provides a method and device which are suitable for an automatic production line, in which the material to be soldered is not damaged during disturbances of the processing sequences and in which no shaking or jarring motions occur during critical soldering phases.
Accordingly, an object of the invention is to provide a method for reflow soldering and reflow desoldering of circuit boards using infrared radiation from radiator groups in a furnace which comprises introducing the circuit boards in a first phase into the furnace, in a second phase selectively either soldering or desoldering the circuit boards as the case may be, in a third phase removing the boards from the furnace and wherein in a first intermediary phase prewarming the circuit boards in the furnace between the first and second phases, and in a second intermediary phase between the second and third phases cooling the circuit boards while they are still in the furnace and wherein the circuit boards both while they are prewarmed and cooled down in the intermediary phases and in the soldering or desoldering first phases stationary in the furnace; and generating infrared radiation substantially only during the first intermediary phase and the second stage.
A further advantageous consideration of the inventive method is that the infrared radiation is substantially homogeneous and is formed by a multitude of parallel thermal rays arranged in radiator groups which extends perpendicular to respective upper and lower sides of the circuit boards.
A further object of the invention is to provide an apparatus with soldering and desoldering circuit boards which comprises an infrared furnace with a conveyor extending through the furnace having its own drive system which carries the circuit boards past a plurality of infrared area radiators arranged in spaced relationship along the furnace. Each of the radiators have their own regulating circuits for its operating current. Means for generating a gas stream are provided with a horizontal flow direction first to the direction of movement to the conveyor. The furnace has a first duct with a ventilator fan for drawing in the gases on a side of the conveyor and a second ventilator fan for drawing off the gases and the soldering vapors on the other side of the conveyor and wherein each of the ventilating fans has a regulating circuit for driving the fans.
A further object of the invention is to provide a device for soldering and/or desoldering circuit boards which is simply in design, rugged in construction, and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.